The present invention generally relates to vehicle braking and, more particularly, to an anti-lock brake control system.
Many automotive vehicles are equipped with an anti-lock brake system (ABS) which modulates the brake force actuation to control the amount of tire slip between the tire and the road surface, in order to maintain stability of the vehicle during braking. Conventional brake systems generate a braking force at the wheels of the vehicle, in response to the vehicle operator depressing a brake pedal, which, in turn, resists rotation of the wheels and creates a deceleration force at the tire and driving surface interface. If the tire slips beyond a certain amount, the braking force between the tire and the driving surface is controlled to reduce the tire slip on the driving surface so as to maintain vehicle stability during vehicle braking. As each tire approaches or exceeds the peak of a mu-slip curve, electronic control is employed to maintain lateral force generating potential. As the tire slip rate increases past the peak on the slip curve, the wheels may lock up, thereby creating possible vehicle instability.
Typical anti-lock brake systems prevent the wheels from locking by reducing the brake force applied to the wheels by modulating the brake force. As a consequence, the brake force is repeatedly increased and decreased in a cyclical fashion. In order to maintain stability of the vehicle, most anti-lock brake systems do not maximize vehicle braking. Instead, current anti-lock brake control systems limit tire slip during straightline bEing to the detriment of decreased stopping distances, in case the driver should command a change in direction (i.e. yaw) as occurs when the steering wheel is turned.
Accordingly, there is a need for an anti-lock brake control system in a vehicle that enhances the vehicle braking to maximize vehicle braking capabilities, particularly when the vehicle is concurrently commanded to travel in a straightline trajectory.
In accordance with the teachings of the present invention, an anti-lock brake control system is provided for a vehicle having a wheel and a brake for applying braking force to the wheel in response to an operator brake command input. The brake control system includes an operator input for commanding vehicle braking, and a brake actuator for applying braking force to the wheel in response to the operator input. In addition, the control system includes a steering angle sensor for sensing a steering angle, and a wheel speed sensor for sensing rotational speed of the wheel. Further, the brake control system includes a controller for controlling the amount of brake force applied by the brake actuator in accordance with a tire slip as determined by the sensed wheel speed. The controller determines the tire slip during braking and increases the tire slip to increase vehicle braking when the vehicle is commanded to travel in a substantially straight line. Accordingly, the brake control system of the present invention optimizes vehicle braking when the vehicle is commanded to travel in a substantially straight line.